In traditional IEEE 802.11 based systems, when node density is high, concurrent broadcast transmissions tend to lack spatial separation. Synchronous systems overcome this drawback by using a hierarchical synchronous periodic channel structure. In such systems, nodes find a primary sub-resource (or slot) to transmit within each broadcast interval (K slots) in a distributed manner with the intervals recurring over time. Thus, the selected slot used by a device is a recurring communications resource.
For selecting and re-selecting the primary resource in a distributed manner, a node may sense the channel at different points in time, e.g., periodically. Since a node cannot sense while it is transmitting, to sense the primary resource, it typically remains silent or transmits in a secondary resource during these update intervals. However, both of these methods have drawbacks. If the node is silent during an entire interval, the overhead is significant, and more importantly, it may not be able to meet the requirement of transmitting in every broadcast interval imposed by systems such as safety broadcast in IEEE 802.11p. Instead, if the node transmits on a secondary resource during update intervals, the performance tends to degrade both in the primary and secondary resources due to the reduction in the number of effective sub-resources and/or poor spatial separation among transmitting nodes.
In view of the above discussion it should be appreciated that there is a need for improved methods and/or apparatus which allow a device to sense channel and/or other conditions without having to let an entire transmission interval go to waste and/or without requiring the use of a secondary alternative resource for transmission purposes while measurements are made in the primary resource, e.g., time slot. It would be desirable, from the perspective of accurately estimating channel conditions, if in it at least some, but not necessarily all time intervals, if the channel sensing was performed when it is likely that other devices, e.g., peer to peer devices using the same resource, were transmitting.